An Alternative Approach to PEPPSI Catalysts: From Palladium Isonitriles to Highly Active Unsymmetrically Substituted PEPPSI Catalysts

A series of new pyridine‐enhanced precatalyst preparation, stabilization, and initiation (PEPPSI)‐type complexes bearing different types of carbene ligands was prepared by the modular and convergent template synthesis strategy. Nitrogen acyclic carbenes, saturated and unsaturated five‐membered NHC, saturated six‐membered NHCs, and five‐membered N‐heterocyclic oxo‐carbene (NHOC) ligands on palladium were prepared this way. These new organometallic compounds then were tested in Suzuki and Negishi cross‐coupling reactions by using substrates with one or two substituents in ortho‐position of the new C?C bond being formed. Both aryl chlorides and bromides were tested as coupling partners. In some cases, the new ligands gave results similar to Organ’s successful IPr‐based and IPent‐based PEPPSI derivatives, with aryl bromides 0.05 mol % catalyst load still gave satisfactory results, with aryl chlorides 0.5 mol % were needed.